Curved stereotype printing plate



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E a I e ai 0 b 2 C c y Patented Mar. 9, 1937 UNITED STATES PATENT OFFICE William Gerrard, Timperley,

to Wood Newspaper England, assignor Machinery Corporation,

New York, N. Y., a corporation of Virginia Application November 1, 1935, Serial No. 47,830 In Great Britain November 6, 1934 6 Claims.

This invention relates to stereotype printing plates which are cast with a curvature corresponding to that of the cylinder of the printing press on which they are to be used. Such stereotype plates are usually formed on their concave surfaces with a number of longitudinally spaced circumferential ribs extending from edge to edge of the plate and of uniform cross section throughout, the inner surfaces of which are formed toV 1o t onto the printing press cylinder.

It is a common practice, more especially in the case of plates of substantially semi-cylindrical form, for the curvature of the ribs to be of slightly smaller radius than that of the surface of the printing cylinder in order to ensure close fitting of the plate on the said cylinder. As a result of this practice, owing to the pressure of the plate on the cylinder being greater at its edges than elsewhere, a bending moment is exerted on the plate which is at a maximum at the centre thereof, and consequently there may be a tendency to distort the curvature of the printing surface of the plate.

According to the invention such tendency to distortion is avoided by providing a greater amount of rib metal n the region of the centre of the plate than at its edges.

In carrying out the invention additional circumferential ribs may be provided which, instead of extending from edge to edge of the plate, ex-

tend over only a portion thereof in the region of its centre; or ribs extending from edge to edge of the plate may be Wider in the region of the plate centre than at the edges. A variation of the strength ofthe plate at different distances from the centre approximating to the variation of the bending moment at the respective parts may be obtained by forming the before-mentioned additional ribs of different lengths or by progressively decreasing the width of the full length ribs from the centre of the plate towards its edges.

The invention is illustrated in ing drawing, in which:-

Figure l is a diagram indicating variations of the bending moment acting at diiferent parts of the plate during its application to the printing press cylinder;

Figure 2 is a similar diagram representing the possible distortion of a plate of ordinary form when it is pushed home on the cylinder;

Figure 3 is a perspective View of one form of improved plate according to the invention, and

Figure 4 is a corresponding perspective view of an alternative constructional form.

the accompany- Referring to Figure 1, a plate l having circumferential ribs 2, of known form is here represented in the position in which it is first applied to the cylinder 3, the radius a of the inner surface of the plate ribs being slightly less than the 5 radius b of the cylinder. It will be recognized that the pressure on the plate at its edges C as lt is brought down on to the surface of the cylinder will exert a bending moment at different parts of the plate varying with the distance of the 10 respective parts from the plate edge; for example, the bending moments at the parts D, E (Figure l) are proportionate to the distances d, e respectively. In other words, the bending moment decreases progressively from the centre to 15 the edges of the plate. There is thus a tendency for the plate to be distorted in the manner represented in Figure 2 producing gaps F beneath the plate midway between the edges and the centre thereof and throwing the printing surface of the 20 plate out of the true semi-cylindrical form.

One constructional form of plate which counteracts this tendency to distortion, is illustrated in Figure 3. In the said constructional form the usual full length circumferential ribs 2 formed 25 on the concave surface of the plate are supplemented by short circumferential ribs 4, 5, located between the full length ribs v2, and disposed symmetrically relatively to the longitudinal centre of the plate, thus providing additional rib 30 metal in the region of the said centre and strengthening the resistance of the plate to bending at the part where the bending moment is greatest.

By arranging the short ribs 4 in alternation 35 with somewhat longer ribs 5 between the full length ribs 2 as shown in the drawing, the variation n the strength of the plate at different distances from the centre may be made to approximate to the variation of the bending mo- 40 ment at the respective parts.

According to the alternative constructional form of the invention illustrated in Figure 4, circumferential ribs 6 extending from edge to edge of the plate progressively decrease in width 45 from the centre towards the edges, the additional rib metal necessary for the purposes of the present invention being thus applied to the respective parts approximately proportionately to the bending moment to which the plate is subjected 5o at those parts.

It will be understood that the diiferent forms of circumferential ribs according to the invention may be readily produced by a corresponding' formation of the circumferential grooves in the 56 core of the casting boX employed for the casting of the plates. Moreover, it is to be noted that the constructional forms of the improved plate above referred to are described and illustrated merely as convenient examples, the number and form of the ribs being variable within the scope of the invention which demands only that additional rib metal be applied in the region of the centre of the plate,

Having described my invention, I declare that what I claim and desire to secure by Letters Patent isz- 1. A curved stereotype printing plate having on its concave surface a plurality of longitudinally spaced circumferential ribs presenting a greater amount of rib metal longitudinally of the plate in the region of the centre of the plate than at the edges thereof.

2. A curved stereotype printing plate formed on its concave surface With a plurality of longitudinally spaced circumferential ribs, said ribs comprising long ribs extending from edge to edge of the plate and shorter ribs extending over only a portion of the plate in the region of its centre.

3. A curved stereotype printing plate formed on its concave surface With a plurality of longitudinally spaced long circumferential ribs extending from edge to edge of the plate, and a plurality of shorter circumferential ribs located between the long ribs extending over only a portion of the plate in the region of its centre.

4. A curved stereotype vprintingl plate according to claim 3, wherein the shorter ribs are of respectively different lengths and disposed Symmetrically relatively to the longitudinal centre of the plate.

5. A curved stereotype printing plate having on its concave surface a plurality of longitudinally spaced circumferential ribs extending from edge to edge of the plate each rib being of greater width in the region of the centre of the plate than at its edges.

6. A curved stereotype printing plate according to claim 5, wherein the circumferential ribs progressively decrease in Width from the centre of the plate towards the edges thereof.

WILLIAM GERRARD. 

